This invention relates generally to inkjet printhead fabrication processes and more particularly to methods for fabricating fully integrated inkjet printheads on a substrate.
There are known and available commercial printing devices such as computer printers, graphics plotters and facsimile machines which employ inkjet technology, such as inkjet pens. An inkjet pen typically includes an ink reservoir and an array of inkjet printing elements. The array is formed by an inkjet printhead. Each printing element includes a nozzle chamber, a firing resistor and a nozzle opening. Ink is stored in the reservoir and passively loaded into respective firing chambers of the printhead via an ink refill channel and respective ink feed channels. Capillary action moves the ink from the reservoir through the refill channel and ink feed channels into the respective firing chambers. Printer control circuitry outputs respective signals to the printing elements to activate corresponding firing resistors. In response an activated firing resistor heats ink within the surrounding nozzle chamber causing an expanding vapor bubble to form. The bubble forces ink from the nozzle chamber out the nozzle opening. An orifice plate adjacent to the barrier layer defines the nozzle openings. The geometry of the nozzle chamber, ink feed channel and nozzle opening defines how quickly a corresponding nozzle chamber is refilled after firing.
To achieve high quality printing ink drops or dots are accurately placed at desired locations at designed resolutions. Printing at resolutions of 300 dots per inch and 600 dots per inch is known. Higher resolutions also are being sought.
A monolithic structure for an inkjet printhead is described in copending U.S. patent application Ser. No. 08/597,746 filed Feb. 7, 1996 for "Solid State Ink Jet Print Head and Method of Manufacture." The process described therein includes photoimaging techniques similar to those used in semiconductor device manufacturing. The printing elements of a monolithic printhead are formed by applying layers to a silicon die. The firing resistors, wiring lines and nozzle chambers are formed by applying various passivation, insulation, resistive and conductive layers on the silicon die. Such layers are referred to collectively as a thin film structure. An orifice plate overlays the thin film structure opposite the die. Nozzle openings are formed in the orifice plate in alignment with the nozzle chambers and firing resistors. The geometry of the orifice openings affect the size, trajectory and speed of ink drop ejection. Orifice plates often are formed of nickel and fabricated by lithographic and electroforming processes.